1. Field of the Invention
This invention relates to optical fibre cable and more particularly although not exclusively to such cable for blown installation.
2. Description of the Related Art
One method of installing an optical fibre cable in a duct comprises blowing the cable into the duct using gaseous flow which is fed into an inlet end of the duct together with the cable. The length of cable which can be blown into the duct can be increased by applying an additional pushing force to the cable at the inlet end of the duct. Optical fibre cables for blown installation do not have to withstand high tensile loads (unlike cables which are to be pulled through ducting) but they do require a degree of stiffness for the application of the pushing force.
A design of optical fibre cable marketed by Pirelli Cables Ltd under the designation ‘Multi-Element Loose Tube’ (MLT) is shown in FIG. 1 and has a core 10 comprising a plurality of tubes 12 stranded about a central solid strength member 14 and a plurality of optical fibres 16 in each tube 12, and a jacket 18 surrounding said core 10. An aluminium/plastics laminate tape 20 surrounds the tubes to retain the same about the strength member 14 and also to act as a moisture barrier and, because it is electrically conductive, to enable location of the cable to be detected. Also spaces within each tube which would otherwise be void are filled with a water blocking material 22.